phases: move pure phase computation in a function

mercurial/phases.py

@@ -179,11 +179,7 class phasecache(object):
             nativeroots.append(map(repo.changelog.rev, self.phaseroots[phase]))
         return repo.changelog.computephases(nativeroots)
 
-    def getphaserevs(self, repo):
-        if self._phaserevs is None:
-            try:
-                self._phaserevs = self.getphaserevsnative(repo)
-            except AttributeError:
+    def computephaserevspure(self, repo):
                 repo = repo.unfiltered()
                 revs = [public] * len(repo.changelog)
                 self._phaserevs = revs
@@ -195,6 +191,13 class phasecache(object):
                             revs[rev] = phase
                         for rev in repo.changelog.descendants(roots):
                             revs[rev] = phase
+
+    def getphaserevs(self, repo):
+        if self._phaserevs is None:
+            try:
+                self._phaserevs = self.getphaserevsnative(repo)
+            except AttributeError:
+                self.computephaserevspure(repo)
         return self._phaserevs
 
     def invalidate(self):